You can easily enable pickups based upon a customer's tag by using the code shown below.
Place this code in the storepickup-addons.liquid file in your theme.
{% assign disable_pickups = true %}
{% if customer %}
{% if customer.tags contains "Pickup Allowed" %}
{% assign disable_pickups = false %}
{% endif %}
{% endif %}
In this example, in-store pickup would be disabled by default and not appear as an option on your shopping cart page. In-store pickup would only be visible if your customer was logged in and had the tag “Pickup Allowed”.